Crawlspace Insulation — Wall or Floor?
Hi
I have been reading up on ventless closed crawlspaces and am convinced it is what I should retrofit to my circa 1971 home in Richmond Virginia. Condensation, rot, and mold are not a problem, but the house has always felt cold. So my primary goal in doing the crawlspace work is for energy efficiency, but going ventless with good sealing on all vapor barriers and conditioning the crawlspace air will be completed as well.
My contractor has more experience installing insulation bats between the floor joists. I read a lot of opinions on insulating the crawlspace walls instead. My walls are 8″ cinderblock with full-depth brick veneer on the outside. The crawlspace.org website resources state that insulation value is roughly the same regardless of where the insulation is placed — walls or floor. My contractor looked at my wall thickness and thought insulating the walls would not add much value, and so he recommends insulating the floors with R-19 bats.
Assume the area to be insulated is a 40 foot x 40 foot crawlspace with an average wall height of 30 inches.
What do folks think — taking into account cost, effort, and return on energy savings, should I teach my contractor how do insulate the crawlspace walls, or do the floors? (my contractor is a fast learner and won’t balk at my requests). Either way, what thickness of insulation / R value should we use?
Replies
I'd consider rigid or spray foam on the walls, minimum of two inches. A couple of inches of rigid foam on the slab wouldn't hurt either. Keeping the crawl space within the thermal envelope seems to be the recommendation these days.
I should have clarified that there is no slab, only dirt throughout the original foundation and the addition.
All the more reason to do the walls, but run poly sheeting over the bed and up the block walls first. Then rigid foam on the walls.
Good luck,
"rigid foam on the walls"
Does the foam need fire proof cover on the face???( I thought it did)bud
I'd get a good radon test done before incorporating 1600 sqft of dirt into conditiond space.
Something like one of these should do for him.
http://www.radonzone.com/store.html
I had an almost identical situation as yours. 30" crawl, on gravel with block walls. Climate almost the same as Richmond but a little cooler (Middleburg, VA.).
I insulated the walls instead of the floor largly because it saved me $700 in insulation costs. For the 17 years I lived there it worked perfect. Wanted to monitor the temp so I bought an indoor/outoor temp. guage, installed it in a kitchen base cabinet with the outdoor componant hanging down in the crawl and it stayed at a constant 60DF.
We had HVAC ducts there with no vents and I think the residual heat from them kept it from getting cooler in the winter.
Runnerguy
Walls. Less cost, more effective -
"Ask not what the world needs. Ask what makes you come alive... then go do it. Because what the world needs is people who have come alive."
Howard Thurman
I just bought 45 sheets of 2" rigid insulation to do my walls and (most importantly) my joist bays atop the walls.....so I say do the walls.
I hooked up with a local commercial/retail demolition crew that sold me the sheets used for $400; only thing wrong with them is some dabs of glue on the back, to buy new is $25/sheet.
I figure if I were to insulate the floor, then I gotta insulate the ducts, should then up the insulation in the ceiling....and would probably end up with a colder floor. So I decided to just insulate and "heat" the crawlspace by not insulating the ducts. My well is under the hose anyway so now it won't freeze. Floors are warm and crawlspace is dryer.
BTW: if you "heat" your crawlspace be aware you must have a very,very,very good vapor barrier on the floor. If you do not you will have a subterranean mushroom garden under there.....I'm talkin' HUGE mushrooms.
BTW #2: if you "heat" your crawlspace you must also insulate the COLD water lines. If you do not, you will drip water from all the elbows via condensation. Water=humidity=mushrooms.
GK
What kind of mushrooms? I just payed $20/lb for Chanterelles at Whole Foods.I am also considering changing out my FG for foam in my heated crawl spaces as it has become mouse city.Awhile back I saw a dumpster full of 2" foam, perfectly stacked up on edge. Gawd I wanted that stuff, but it was in the city and I had nowhere to put it."We don't throw the first punch, but we'll throw the last" Barack Obama Oct.2008
You should have been around here after the remnents of Ike blew through. My concrete materials supply is three blocks from where I work. They always have a yard full of 2" blue board. You could have picked up a couple of bunkers of it along the street and RR tracks. I saw full sheets of it almost three miles from the yard.
I always used R-11 or R-13 FSK foil faced fiberglass on the block walls nailed with hilti with large washers.
All our insulators did it and I am sure that many in your region do it.
A lot of the big builders down your way used to (and maybe still do) nail it to the walls.
Lots of foam boards these days and people like them but I dont know the benefits of either other than foam is better if moist, but you would want to control moisture anyway in the crawl so I would want at least a vapor barrier on the floor at a minimum.
I would stay away from fiberglass on the walls. I was in a crawlspace two days ago that had foil-faced FG on the walls and they were soaking wet from condensation. Rigid foam is a much better choice, but it should technically be covered with a fire retardant. A good vapor barrier on the floor is a must.
when we bought our house, it had FG in the crawlspace in the joist bay ends. All was fully saturated. Not only did this rot all the bonds, it also bred mosquitos. Our house would be full of mosquitos all year long. Imagine in the dead of winter to wake in the middle of the night from a mosquito attack.Vermin love FG too. Keeps them warm and cozy. Oh, and there was the joist bay that was a bee hive. I got rid of all the FG under floor. What fire retardant would you use in a crawlspace and why?GK
Edited 11/15/2008 8:37 am ET by Dreamcatcher
If an electrician were to crawl in there and light a cigarette or if a halogen light were to lean against the foam it could catch on fire. I've had it happen to me soldering pipes with foam right behind the pipes. For some reason I didn't think the foam was flammable but it sure was.
Open cell foam I believe is not flammable, but don't quote me on that.
The fireproof layer could be what's called intumescent paint, or a layer of sheetrock (moisture resistant!), or stucco, or plywood. The paint is probably the easiest but also the most expensive.
Something like this?
http://www.firefree.com/?utm_source=Google&utm_medium=PPC&utm_content=Foam&utm_campaign=Foam
What would it cost to cover say 600 sq. ft.
That's the product, but I don't know the cost. I've only used it once on a job and the spray foam guys included it in their price.